This invention relates to food processing and particularly, heating or cooking raw or fresh foods. The apparatus and method according to the invention have particular application in heating meat to produce formed meat products.
Cooking a fresh or raw foodstuff changes its composition and characteristics. The cooking process requires heating the food material to some cooking temperature for a cooking period. The cooking temperature varies for different foods as does the cooking period. Regardless of the cooking temperature or period, the heat may be applied to the foodstuff directly in a suitable oven or through a container which holds the foodstuff.
There are a number of problems associated with many traditional foodstuff heating and cooking methods, particularly when applied to meats, including fish and poultry. One problem is volume and water loss during the heating process. In many traditional cooking methods, the foodstuff is open to the atmosphere as it goes through the relatively slow heating process. This allows significant water loss, reduces the volume of the final cooked product, and often makes the cooked product less desirable. This water and volume loss from heating is commonly referred to as cooking loss.
Another problem is that some prior heating techniques allowed the food material to cook or burn onto the container in which it was held during heating. The foodstuff had to be moved or stirred continuously to avoid this "cook on" or "burn on" and produce even heating through the product.
Cooking meat products made up of small pieces of meat poses additional problems. When a collection of meat pieces is heated in a traditional cooking technique, the pieces tend to separate. For example, unless it is carefully formed and handled, ground beef breaks up into the individual grinds upon cooking. This separation into individual grinds is a particular problem in prior continuous cooking devices which used blades to periodically scrape the device walls to prevent burn on. Even when formed and handled properly, the resulting cooked patty has a character entirely different from a solid piece of meat. That is, it is apparent from the texture and other characteristics of the cooked patty that it is made up of individual small pieces placed together for cooking.
Processes have been developed for producing formed meat products having characteristics more resembling a solid, traditional cut of meat. These forming processes produce a protein/meat surface interaction which may form a bond between adjacent pieces or chunks of meat in a mixture.
In these meat forming processes, a surface protein matrix is obtained using natural protein from the meat, or non-meat protein additives. The natural meat proteins for this process comprise the myofibrillar proteins, particularly myosin. These natural proteins are brought to the surface of the meat pieces by manipulating the meat pieces and, in some cases, by adding salt or otherwise chemically treating the mixture.
Once the surface protein matrix is produced in the mixture and the mixture is formed into the desired shape, the mixture is heated to at least partially de-nature the proteins. Upon cooling, the protein matrix coagulates and this coagulation binds the meat pieces together. The final internal temperature required to produce the desired coagulation upon cooling may range from 135.degree. F. to 155.degree. F. This temperature range is the range in which most myofibrillar proteins are heat de-natured and is also sufficient to cook the meat, that is, convert the oxymyoglobin in the meat to metamyoglobin.
These prior art meat forming processes are relatively slow and complicated and, therefore, expensive. Furthermore, the forming processes do not address the problem of cooking loss or of cook-on or burn-on, which may occur during the heating process.